1. Field of the Invention
The present invention relates to a gate drive circuit of a power semiconductor module, comprising a power semiconductor switching device having connected thereto in parallel a freewheeling diode having a small reverse recovery current such as a Schottky barrier diode of a wide bandgap semiconductor such as SiC and GaN or a PiN diode of a wide bandgap semiconductor, and an inverter circuit comprising the same.
2. Description of the Related Art
FIG. 5 shows a circuit diagram of a common inverter using IGBTs (insulated gate bipolar transistors). The inverter is composed of six IGBTs and diodes, and power is supplied from a main circuit power supply to a load motor by alternately switching the IGBTs on the upper arm and the lower arm. There are demands to reduce conduction loss and switching loss caused by the IGBTs and diodes in the inverter device. In order to reduce such losses, it is necessary to improve the structure of the IGBT so as to reduce the on-voltage, or to improve the drive circuit of the IGBT to enable the IGBT to be driven at high speed. PiN diodes formed of Si are generally used as the diodes.
FIG. 6 shows a circuit diagram of the IGBT corresponding to a single phase, and a recovery waveform of an upper diode and a turn-on waveform of a lower IGBT when the lower IGBT is turned on. By driving the IGBT at high speed (solid line waveform) which is faster than normal drive speed (dotted line waveform), the di/dt of the IGBT during turn-on is increased, and both the turn-on loss and the recovery loss can be reduced. However, the di/dt of the reverse recovery of the PiN diode is also increased, and the current change (reverse recovery di/dt) during attenuation of the reverse recovery current of the PiN diode is multiplied with the main circuit inductance L to create a commutation surge (ΔVp=L×reverse recovery di/dt), wherein when the sum (E+ΔVp) of the power supply voltage (E) and the surge voltage (ΔVp) exceeds the withstand voltage of the power semiconductor switching device, the power semiconductor device may be damaged. Therefore, arts related to reducing the inductance of the main circuit and arts related to varying the turn-on di/dt have been proposed.
For example, Japanese patent No. 3161589 (patent document 1) discloses an art of detecting the recovery current of a freewheeling diode, and switching the turn-on di/dt in two steps to thereby reduce both the turn-on loss and the surge voltage.
Further, Japanese patent No. 3941309 (patent document 2) discloses an art of controlling the turn-on gate drive speed in three steps (high speed, low speed, and high speed) so as to solve the problem of high dv/dt generated when the turn-on di/dt is set to high speed, which causes a noise in the range of over a few MHz and causes erroneous operation of peripheral devices, and to realize both noise reduction in the high frequency range and loss reduction.
As described above, according to the prior art IGBT inverter and the inventions disclosed in patent documents 1 and 2, attempts were made to reduce both the turn-on loss and the surge voltage or to reduce both the noise in the high frequency range and the loss by varying the gate charge speed. However, there were drawbacks according to the Si-PiN diode in which the recovery current became high when a large amount of current was conducted, and a large surge voltage was generated when a small current was conducted for a short period of time.